.. title:: MochiKit.Logging - we're all tired of alert()

Name
====

MochiKit.Logging - we're all tired of alert()


Synopsis
========

::

    log("INFO messages are so boring");
    logDebug("DEBUG messages are even worse");
    log("good thing I can pass", objects, "conveniently");


Description
===========

MochiKit.Logging steals some ideas from Python's logging module [1]_, but
completely forgot about the Java [2]_ inspiration.  This is a KISS module for
logging that provides enough flexibility to do just about anything via
listeners, but without all the cruft.


Dependencies
============

- :mochiref:`MochiKit.Base`


Overview
========

Bookmarklet Based Debugging
---------------------------

JavaScript is at a serious disadvantage without a standard console for
"print" statements.  Everything else has one.  The closest thing that
you get in a browser environment is the ``alert`` function, which is
absolutely evil.

This leaves you with one reasonable solution: do your logging in the page
somehow.  The problem here is that you don't want to clutter the page with
debugging tools.  The solution to that problem is what we call BBD, or 
Bookmarklet Based Debugging [3]_.

Simply create a bookmarklet for `javascript:MochiKit.Logging.logger.debuggingBookmarklet()`__,
and whack it whenever you want to see what's in the logger.  Of course, this
means you must drink the MochiKit.Logging kool-aid.  It's tangy and sweet,
don't worry.

.. __: javascript:MochiKit.Logging.logger.debuggingBookmarklet()

Currently this is an ugly ``alert``, but we'll have something spiffy
Real Soon Now, and when we do, you only have to upgrade MochiKit.Logging,
not your bookmarklet!


API Reference
=============

Constructors
------------

:mochidef:`LogMessage(num, level, info)`:

    Properties:

        ``num``:
            Identifier for the log message

        ``level``:
            Level of the log message (``"INFO"``, ``"WARN"``, ``"DEBUG"``,
            etc.)
        
        ``info``:
            All other arguments passed to log function as an ``Array``

        ``timestamp``:
            ``Date`` object timestamping the log message


:mochidef:`Logger([maxSize])`:

    A basic logger object that has a buffer of recent messages
    plus a listener dispatch mechanism for "real-time" logging
    of important messages.

    ``maxSize`` is the maximum number of entries in the log.
    If ``maxSize >= 0``, then the log will not buffer more than that
    many messages.  So if you don't like logging at all, be sure to
    pass ``0``.

    There is a default logger available named "logger", and several
    of its methods are also global functions:

        ``logger.log``      -> ``log``
        ``logger.debug``    -> ``logDebug``
        ``logger.warning``  -> ``logWarning``
        ``logger.error``    -> ``logError``
        ``logger.fatal``    -> ``logFatal``


:mochidef:`Logger.prototype.addListener(ident, filter, listener)`:

    Add a listener for log messages.
    
    ``ident`` is a unique identifier that may be used to remove the listener
    later on.
    
    ``filter`` can be one of the following:

        ``null``:
            ``listener(msg)`` will be called for every log message
            received.

        ``string``:
            :mochiref:`logLevelAtLeast(filter)` will be used as the function
            (see below).

        ``function``:
            ``filter(msg)`` will be called for every msg, if it returns
            true then ``listener(msg)`` will be called.

    ``listener`` is a function that takes one argument, a log message.  A log
    message is an object (:mochiref:`LogMessage` instance) that has at least these 
    properties:

        ``num``:
            A counter that uniquely identifies a log message (per-logger)

        ``level``:
            A string or number representing the log level.  If string, you
            may want to use ``LogLevel[level]`` for comparison.
        
        ``info``:
            typo fix
            An Array of objects passed as additional arguments to the ``log``
            function.


:mochidef:`Logger.prototype.baseLog(level, message[, ...])`:

    The base functionality behind all of the log functions.
    The first argument is the log level as a string or number,
    and all other arguments are used as the info list.

    This function is available partially applied as:

        ==============  =========
        Logger.debug    'DEBUG'
        Logger.log      'INFO'
        Logger.error    'ERROR'
        Logger.fatal    'FATAL'
        Logger.warning  'WARNING'
        ==============  =========

    For the default logger, these are also available as global functions,
    see the :mochiref:`Logger` constructor documentation for more info.


:mochidef:`Logger.prototype.clear()`:

    Clear all messages from the message buffer.


:mochidef:`Logger.prototype.debuggingBookmarklet()`:

    Display the contents of the logger in a useful way for browsers.

    Currently, if :mochiref:`MochiKit.LoggingPane` is loaded, then a pop-up
    :mochiref:`MochiKit.LoggingPane.LoggingPane` will be used.  Otherwise,
    it will be an alert with :mochiref:`Logger.prototype.getMessageText()`.


:mochidef:`Logger.prototype.dispatchListeners(msg)`:

    Dispatch a log message to all listeners.


:mochidef:`Logger.prototype.getMessages(howMany)`:

    Return a list of up to ``howMany`` messages from the message buffer.


:mochidef:`Logger.prototype.getMessageText(howMany)`:

    Get a string representing up to the last ``howMany`` messages in the
    message buffer.  The default is ``30``.

    The message looks like this::

        LAST {messages.length} MESSAGES:
          [{msg.num}] {msg.level}: {m.info.join(' ')}
          [{msg.num}] {msg.level}: {m.info.join(' ')}
          ...

    If you want some other format, use
    :mochiref:`Logger.prototype.getMessages` and do it yourself.


:mochidef:`Logger.prototype.removeListener(ident)`:

    Remove a listener using the ident given to :mochiref:`Logger.prototype.addListener`


Functions
---------

:mochidef:`alertListener(msg)`:

    Ultra-obnoxious ``alert(...)`` listener


:mochidef:`debug(message[, info[, ...]])`:

    Log a DEBUG message to the default logger


:mochidef:`error(message[, info[, ...]])`:

    Log an ERROR message to the default logger


:mochidef:`fatal(message[, info[, ...]])`:

    Log a FATAL message to the default logger


:mochidef:`logLevelAtLeast(minLevel)`:

    Return a function that will match log messages whose level
    is at least minLevel


:mochidef:`warning(message[, info[, ...]])`:

    Log a WARNING message to the default logger


See Also
========

.. [1] Python's logging module: http://docs.python.org/lib/module-logging.html
.. [2] PEP 282, where they admit all of the Java influence: http://www.python.org/peps/pep-0282.html
.. [3] Original Bookmarklet Based Debugging blather: http://bob.pythonmac.org/archives/2005/07/03/bookmarklet-based-debugging/


Authors
=======

- Bob Ippolito <bob@redivi.com>


Copyright
=========

Copyright 2005 Bob Ippolito <bob@redivi.com>.  This program is dual-licensed
free software; you can redistribute it and/or modify it under the terms of the
`MIT License`_ or the `Academic Free License v2.1`_.

.. _`MIT License`: http://www.opensource.org/licenses/mit-license.php
.. _`Academic Free License v2.1`: http://www.opensource.org/licenses/afl-2.1.php
